Stroke adjustment mechanism for reciprocating pumps

ABSTRACT

A stroke adjustment mechanism having fewer parts that are easier to manufacture. In order to translate stroke adjustment into an eccentric offset of a rotating shaft to act as a rotating cam surface, the present invention utilizes two separate and identical plungers. The plungers are easier to manufacture as they do not require complex machining in mating parts. The present invention is also easier to assemble than prior designs. The present invention allows the drive gear to be produced with a simple round ID bore and also uses a one-piece, easy to machine round shaft. This provides for a simple and strong design.

CROSS REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Patent Application No. 60/922,048 filed on Apr. 5, 2007, entitled Stroke Adjustment Mechanism for Reciprocating Pumps, which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to reciprocating pumps and particularly to a stroke adjustment mechanism suitable for use with a reciprocating pump.

BACKGROUND OF THE INVENTION

Stroke adjustment mechanisms are used to control the output of a reciprocating pump by changing the length of the plunger or piston stroke. There are two different types of stroke adjustment mechanisms: lost motion and full motion. The present invention is the full motion type of stroke adjustment mechanism.

Existing designs for stroke adjustment mechanisms suffer from some drawbacks such as difficulty of manufacturing and unnecessary numbers of parts and complexity. Other designs utilize complex bores on the drive gear that are prone to failure. Other designs utilize complex square or weak shaft systems with bolt-on cam pieces. What is needed is an improved design that is easier to manufacture and that utilizes fewer parts.

SUMMARY OF THE INVENTION

The present invention meets the above-described need by providing a stroke adjustment mechanism having fewer parts that are easier to manufacture. In order to translate stroke adjustment into an eccentric offset of a rotating shaft to act as a rotating cam surface, the present invention utilizes two separate and identical plungers. The plungers are easier to manufacture as they do not require complex machining in mating parts. The present invention is also easier to assemble than prior designs. The present invention allows the drive gear to be produced with a simple round ID bore and also uses a one-piece, easy to machine round shaft. This provides for a simple and strong design.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in the drawings in which like reference characters designate the same or similar parts throughout the figures of which:

FIG. 1 is a cross-sectional view of the stroke adjustment mechanism of the present invention used with a diaphragm pump;

FIG. 2 is a cross-sectional view of the stroke adjustment mechanism used with a duplex (two-headed) pump;

FIG. 3 is a cutaway perspective view of the stroke adjustment mechanism of the present invention; and,

FIG. 4 is a perspective view of some of the components of the stroke adjustment mechanism.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIGS. 1-2, the stroke adjustment mechanism of the present invention is shown in connection with a spring-biased plunger 13 coupled to the diaphragm 16 of a pump. The diaphragm 16 is connected to the plunger 13 at a distal end 19. A spring 22 engages a flange 25 to bias the plunger 13 against a rotating cam 28.

The rotating cam 28 controls the stroke of the plunger 13. The stroke adjustment mechanism provides for adjusting the position of the cam 28 relative to a shaft 31. The shaft 31 rotates in a set of bearings 35, 36. A pair of separate and identical plungers 37 are disposed on opposite sides of a sliding member 39 inside the shaft 31. The sliding member 39 has angled surfaces 40 and 43 that engage with angled surfaces 46 and 49 on the plungers 37. The plungers 37 have end walls 52 and 55 that engage with the inside walls of the cam 28. The cam 28 has inside walls 58, 61, 64, and 67 (FIG. 4) that define a rectangular opening 70. The rectangular shape provides for adjustment of the position of the cam 28 relative to the shaft 31 such that an eccentric offset can be achieved. Movement of the sliding member 39 inside the shaft 31 in the direction of axis 73 causes the plungers 37 to move relative to the shaft 31 which because of the engagement between the plungers 37 and the inside wall of the cam 28 causes the cam 28 to move relative to the shaft 31. Accordingly, the cooperating angled surfaces on the plungers 37 and the sliding member 39 provide for adjustment of the position of the cam 28 relative to the shaft 31.

The position of the sliding member 39 can be adjusted in the direction of axis 73 by means of a hand-operated knob 76 attached to shaft 91. The threads 79 on the shaft 91 engage with threads 82 on the inside wall 85 of housing 88. The knob 76 adjusts the position of the shaft 91 that is connected to the sliding member 39 inside the shaft 31. The position of shaft 91 can be changed manually or by other means such as an electric servo motor. The sliding member 39 is connected to the insert member 91 for movement in the direction of axis 73 but is capable of rotating freely with respect thereto by means of bearing 34. The shaft 31 may be rotated in numerous ways as will be evident to those of ordinary skill in the art based on this disclosure.

As shown in FIG. 2, the device is shown in a maximum stroke configuration. If the sliding member 39 is moved from left to right with respect to the orientation of the figure, the angled surfaces 40; 43 of the sliding member 39 will cause the plungers 37 to move upward with respect to the figure therefore adjusting the position of the cam surface 28 relative to the shaft 31.

In FIG. 4, the shaft body 102 is shown with the sliding member 39 removed. The shaft body 102 has a cylindrical bore with a pair of openings 104, 107 for receiving the plungers 37. The sliding member 39 has a round end portion 110 at a first end 113. The angled walls extend from the end portion 110 toward the second end 120.

As shown, the cam 28 has a sleeve 123 disposed on the outer circumference. The rectangular opening receives a substantially square portion 126 of the shaft body 102.

The present invention provides many advantages including that it is simple to machine the shaft and gear. The invention provides a strong one-piece shaft 31. The invention provides a more accurate assembly because there are less assembly clearances. The design is less expensive to manufacture. The design includes two actuator pins. Also, there is no special machining for the gear. No cam surfaces or square or angled bores are required. The eccentric cam ring utilizes a simple symmetrical rectangular bore with straight surfaces centered inside a round outside diameter. Another advantage is that there is no connecting rod so the inherent weakness of a small clevis pin is avoided. However, this design could be used with a connecting rod instead of a spring return plunger/piston, if desired. The entire rotating mechanism can be assembled and zeroed outside the gearbox and installed from the side as one piece. Also, because of the design the present invention can be easily duplexed.

While the invention has been described in connection with certain embodiments, it is not intended to limit the scope of the invention to the particular forms set forth, but, on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 

1. A stroke adjustment mechanism for a reciprocating pump, the stroke adjustment mechanism, comprising: a first plunger; a cam operatively associated with the plunger, the cam having a central opening surrounded by inside walls; a shaft disposed through the opening in the cam, the shaft having a cavity and having a pair of openings disposed in communication with the cavity, the shaft rotating about a fixed axis; a sliding member disposed in the cavity and capable of movement relative to the shaft, the sliding member having a pair of angled surfaces; a pair of second plungers disposed through the openings in the shaft and extending between the inside wall of the cam and the angled surface on the sliding member; and, an adjustment shaft connected to an end of the sliding member, the adjustment shaft connected to the sliding member such that the sliding member is capable of rotating with respect to the adjustment shaft, the adjustment shaft capable of being moved in an axial direction to adjust the position of the sliding member.
 2. The stroke adjustment mechanism of claim 1, wherein each of the second plungers has an angled surface.
 3. The stroke adjustment mechanism of claim 1, further comprising a knob connected to the adjustment shaft.
 4. The stroke adjustment mechanism of claim 3, wherein the adjustment shaft has threads capable of engaging with threads on a housing such that rotation of the cap produces adjustable axial motion of the adjustment shaft.
 5. The stroke adjustment mechanism of claim 1, wherein the angled surfaces on the sliding member are disposed on opposite sides.
 6. The stroke adjustment mechanism of claim 1, wherein the first plunger is spring biased into engagement with the cam.
 7. The stroke adjustment mechanism of claim 1, wherein the cam rotates eccentrically about the shaft.
 8. The stroke adjustment mechanism of claim 1, wherein each of the pair of second plungers is substantially identical.
 9. A stroke adjustment mechanism for a reciprocating pump having a diaphragm, the stroke adjustment mechanism, comprising: a first plunger connected to the diaphragm; a cam spring biased into engagement with the plunger, the cam having a central opening surrounded by inside walls; a shaft disposed through the opening in the cam, the shaft having a cavity and having a pair of openings disposed in communication with the cavity, the shaft rotating about a fixed axis; a sliding member disposed in the cavity and capable of movement relative to the shaft, the sliding member having a pair of angled surfaces; a pair of second plungers with each having a first end with a substantially flat surface and having a second end with an angled surface, the plungers disposed through the openings in the shaft and extending between the inside wall of the cam and the angled surface on the sliding member; and, an adjustment shaft connected to an end of the sliding member, the adjustment shaft connected to the sliding member such that the sliding member is capable of rotating with respect to the adjustment shaft, the adjustment shaft capable of being moved in an axial direction to adjust the position of the sliding member; and, wherein movement of the adjustment shaft in the axial direction causes the sliding member to move in the axial direction, the axial movement of the sliding member causing the second plungers to move in equal and opposite directions substantially perpendicular to the axial direction such that the position of the cam relative to the shaft is adjusted for eccentric rotation.
 10. The stroke adjustment mechanism of claim 9, further comprising a knob connected to the adjustment shaft.
 11. The stroke adjustment mechanism of claim 10, wherein the adjustment shaft has threads capable of engaging with threads on a housing such that rotation of the cap produces adjustable axial motion of the adjustment shaft.
 12. The stroke adjustment mechanism of claim 9, wherein the angled surfaces on the sliding member are disposed on opposite sides.
 13. The stroke adjustment mechanism of claim 9, wherein each of the pair of second plungers is substantially identical.
 14. A shaft assembly for a stroke adjustment mechanism, the shaft assembly comprising: a unitary body having a first end, a second end, a cavity, and a pair of openings in communication with the cavity; a sliding member having a first end and a second end, the sliding member disposed in the body and capable of moving axially relative thereto, the sliding member having a pair of angled surfaces; a pair of plungers having a first end and a second end with an angled surface opposite the first end, the plungers disposed through the openings in the body such that the angled surface on the second ends of the plungers engages with the angled surfaces on the sliding member; and, an adjustment shaft connected to the first end of the sliding member such that the sliding member is capable of rotating with respect to the adjustment shaft, the adjustment shaft capable of being moved in an axial direction to adjust the position of the sliding member.
 15. The shaft assembly of claim 14, further comprising a knob connected to the adjustment shaft.
 16. The shaft assembly of claim 14, wherein the adjustment shaft has threads capable of engaging with threads on a housing such that rotation of the cap produces adjustable axial motion of the adjustment shaft.
 17. The shaft assembly of claim 14, wherein the angled surfaces on the sliding member are disposed on opposite sides.
 18. The shaft assembly of claim 14, wherein each of the pair of plungers is substantially identical.
 19. The shaft assembly of claim 14 further comprising a cam having a central opening for receiving the shaft assembly therethrough.
 20. The shaft assembly of claim 19, wherein the shaft rotates in a set of bearings about a fixed axis and movement of the sliding member causes the plungers to adjust the position of the cam in a direction substantially perpendicular to the fixed axis.
 21. The stroke adjustment mechanism of claim 1, wherein the shaft has a cylindrical end. 